Electronic devices used with wireless communication systems, such as cellular phones, GPS receivers, and Wi-Fi enabled notebook and tablet computers, generally contain signal processing systems that have interfaces to the analog world. Such interfaces may include wire line and wireless receivers that receive transmitted power and convert the received power to an analog or digital signal that may be demodulated using analog or digital signal processing techniques. A typical wireless receiver architecture includes a low noise amplifier (LNA) that amplifies the very small signals that may be received by an antenna and passes an amplified signal to later amplification and/or signal processing stages. By providing gain at the LNA, subsequent gain processing stages are made less sensitive to noise, thereby enabling a lower system noise figure.
In some signal environments, however, the received RF signal may vary over a few orders of magnitude depending on the relative locations of the transmitter and receiver and depending on the amount of power being transmitted. When a mobile device is in close proximity with a transmitting device, the received RF power may be strong enough to saturate an LNA that is configured to amplify weak signals. To address this situation, some RF systems support a “linearity on demand” feature in which the gain of the LNA is decreased to accommodate the increased received signal power. In some systems, the LNA itself may be bypassed to increase system linearity. However, the practical implementation of “linearity on demand” features poses challenges with respect to maintaining an adequate system noise figure and RF match.